The phenomena of light- and dark-adaptation have been studied extensively. However, the description of the adaptive mechanisms of the eye and their place of action is still incomplete. Psychophysical measurements on human subjects yielded two opposing theories. Rushton suggested an automatic gain control box in the neural retina while Barlow placed all the adaptation within the photoreceptors. Electrophysiological evidence based mainly on intracellular recording from the vertebrate retina emphasized the role of the photoreceptors in visual adaptation but did not exclude neural contribution. The proposed research is designed to obtain a complete description of the relative contribution of each retinal level to the overall adaptive behavior of the retina. Intracellular recording from different retinal cells under identical states of adaptation will be compared in order to identify the sites of action of the adaptive mechanisms. It is suggested that in addition to the intrinsic adaptive mechanisms that were previously reported to exist within the photoreceptors some of the neural processing implicated from psychophysical measurements and previous electrophysiological experiments are also present in the photoreceptor cell layer. Lateral interactions arising from coupling between photoreceptors of the same type were found in different species. It is suggested here that cell coupling can serve in pooling signals and that many psychophysical results that formed the basis of the hypothetical neural adaptation can be explained by coupling and can be demonstrated in the distal retina.